In a conventional wireless communication system including a receiver and a transmitter, an automatic frequency correction (AFC) algorithm is used by the receiver for the correction of carrier frequency offset and the sampling clock offset with respect to a transmitter. This is generally performed through the use of pilot signals. However, with the introduction of transmit diversity, high speed data packet access (HSDPA) and the macro-diversity in the wireless communication standards, the AFC algorithm must conform to more stringent requirements introduced by the HSDPA services.
HSDPA services employ higher constellation sizes to produce higher data rates. However, higher constellations are more sensitive to frequency errors. Therefore, HSDPA services require more robust AFC algorithm. On top of these challenges, the AFC algorithm may operate in a macro diversity environment where the receiver processes data from multiple cells at the same time. For example, in a third generation partnership project (3GPP) frequency division duplex (FDD) system, the receiver may receive data from six neighboring cells at the same time. In that case, there are different pilot signals from each cell.
The prior art does not require an AFC algorithm with HSDPA and multiple cell processing capabilities. In general, the prior art does not deal with transmit diversity during AFC initial lock in period (clock synchronization between a wireless transmit/receive unit (WTRU) and a base station). The transmit diversity processing is performed only after the transmit diversity existence is confirmed through the broadcast channel. Therefore, the transmit diversity processing does not contribute to the AFC algorithm during the initial convergence period. This increases the convergence time and decreases the probability of convergence.
The prior art has looser requirements as set by the standards for the transmit frequency error. This is generally sufficient for a receiver with small constellation sizes such as binary phase shift keying (BPSK) or quadrature phase shift keying (QPSK). However, higher constellations at and above 16 QPSK require more stringent requirements. For example, the 3GPP FDD standards require less than 0.1 ppm frequency error in the AFC algorithm. The HSDPA services are noticeably degraded after the frequency error exceeds 0.05 ppm. This requirement forces the AFC algorithm to make efficient usage of the transmit diversity and the macro diversity which were either ignored or unnecessary in the prior art.